Astronomers discover a planet made of diamond

Trent Nouveau, 25th August 2011

An international team of scientists has discovered a planet made of diamond after first detecting a pulsar using the Parkes and Lovell radio telescopes.

Pulsars are essentially small spinning stars approximately 20 km in diameter that emit a beam of radio waves. As the star spins its radio beam sweeps repeatedly over Earth, allowing radio telescopes to pick up a regular pattern of pulses.

However, the arrival times of the pulses emanating from the pulsar - known as PSR J1719-1438 - were markedly and systematically modulated.

Researchers subsequently concluded the deviation was due to the gravitational pull of a small companion planet orbiting the pulsar in a binary system.

According to Professor Bailes of the Swinburne University of Technology in Melbourne, Australia, the pulsar and its planet are part of the Milky Way's plane of stars and lie 4,000 light-years away in the constellation of Serpens (the Snake).

The planet apparently orbits the pulsar in just two hours and ten minutes, as the distance between the two objects is 600,000 km - a little less than the radius of our Sun. Despite its small size (less than 60,00 km), the planet has slightly more mass than Jupiter.

"This high density of the planet provides a clue to its origin," said Professor Bailes, who believes the "diamond planet" is all that remains of a once-massive star - most of whose matter was siphoned off towards the pulsar.

The research team describes Pulsar J1719-1438 as a very fast-spinning pulsar, or millisecond pulsar, as it rotates more than 10,000 times per minute, boasts a mass of about 1.4 times that of our Sun and is only 20 km in diameter.

Interestingly enough, the companion (in its star form), is actually capable of transforming an old, dead pulsar into a millisecond pulsar by transferring matter and spinning it up to a very high speed.

The result? A fast-spinning millisecond pulsar with a shrunken companion - most often a so-called white dwarf.

"We know of a few other systems, called ultra-compact low-mass X-ray binaries, that are likely to be evolving according to the scenario above and may likely represent the progenitors of a pulsar like J1719-1438," explained team member Dr. Andrea Possenti, Director at INAF-Osservatorio Astronomico di Cagliari.

But pulsar J1719-1438 and its companion are so close together that the companion can only be a very stripped-down white dwarf, one that has lost its outer layers and over 99.9% of its original mass.

"This remnant is likely to be largely carbon and oxygen, because a star made of lighter elements like hydrogen and helium would be too big to fit the measured orbiting times," confirmed Dr. Michael Keith of the CSIRO.

The density means the material is certain to be crystalline: that is, a large part of the star may be similar to a diamond.

"The ultimate fate of the binary is determined by the mass and orbital period of the donor star at the time of mass transfer," stated Dr. Benjamin Stappers from The University of Manchester.

"The rarity of millisecond pulsars with planet-mass companions means that producing such 'exotic planets' is the exception rather than the rule, and requires special circumstances."